This invention generally relates to color picture tubes and, more particularly, a method and apparatus for transferring and applying crosswires from a drum unit assembly to a tension mask assembly.
A color picture tube includes an electron gun for forming and directing three electron beams to a screen of the tube. The screen is located on the inner surface of the face plate of the tube and is made up of an array of elements of three different color emitting phosphors. A color selection electrode, also referred to as a shadow mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the tube face plate. A tension mask can be a strand tension mask, tie-bar tension mask or tension focus mask. A tension focus mask comprises two sets of conductive lines that are perpendicular to each other and separated by an insulator. Different voltages are applied to the two sets of lines to create focusing lenses in each of the mask openings. Generally, in a tension focus mask, a vertical set of conductive lines or strands is under tension and a horizontal set of conductive lines or wires overlies the strands.
In assembling a tension focus mask, it is required to assemble the wires and strands with a high degree of accuracy to achieve consistent spacing between the strands and between the wires to optimize visual performance. It is, therefore, desirable to develop techniques for assembling tension focus masks that will provide precise spacing between the vertical conductive elements and between the horizontal conductive element.
The present invention provides a method and apparatus for transferring and attaching crosswires from a drum assembly to a mask frame assembly. The method includes providing a plurality of crosswires that have been rolled onto a drum assembly. The crosswires are then transferred from the drum assembly to a mask frame assembly. In one embodiment, the crosswires are transferred directly onto a mask frame assembly from a drum assembly. In other embodiments, a transfer apparatus is used to transfer the crosswires from the drum assembly to the mask frame assembly.
In the first embodiment, a drum assembly that has had crosswires rolled onto it, unrolls the crosswires onto a mask frame assembly. In this method, both the mask frame assembly and the drum assembly are rotating about a separate different axis point and are moving in a reciprocating manner as the crosswires are transferred from the drum to the mask frame. In a second embodiment, crosswires that have been wound around a drum assembly are cut by a transfer device and moved from the drum assembly onto the mask frame assembly. In a third embodiment, crosswires wound around a drum are transferred from the drum to the mask frame assembly by a mask frame transfer device that contains a self-tensioning device that allows the crosswires to be straightened and tensioned as they are cut from the drum assembly and transferred to a mask frame assembly.